The sizes of solid particles in substances such as in ink, chocolate, and peanut butter has been determined by apparatus called a fineness of grind gage, grind gage or grindometer hereafter referred to as a grindometer, that is comprised of a plate having parallel spaced grooves in a planar surface that gradually vary in depth from one end to the other and a scraper. The scraper is placed in contact with the surface of the plate where the grooves are deepest, and a quantity of the substance to be tested sufficient to fill the grooves is deposited across the grooves in front of it. The scraper is then moved along the surface of the plate toward the shallower ends of the grooves. As the scraper moves along the grooves, it forces the substance under test into them until it meets a particle of such size as to project above the surface in which event it carries the particle along so that the groove is not filled with substance.
It has been customary to move the scraper along the grooves by hand so that the angle of the scraper with respect to the surface of the plate, the angle at which the scraper crosses the grooves, the pressure exerted by the scraper on the plate and the speed with which the scraper moves are extremely variable so that reproduceability of test results is difficult to obtain. Whereas the reproduceability can be improved by a given operator trying to hold these performance parameters within as narrow limits as possible, the results may vary from operator-to-operator.
A machine produced by the Johnsy Gage Manufacturing Company provided some improvement. A grindometer of the type described was mounted on a platform that was moved parallel to the grooves by an electric motor, and a scraper was mounted on a pivoted member that could be rotated so as to bring the scraper into contact with the surface of the grindometer. The force between the scraper and the grindometer was determined by the downward force exerted by an operator on the pivoted member or by a spring. The reproduceability of test results attained by such a machine would be adversely affected by the variability in the force with which the scraper is urged against the grindometer and the fact that the angle of the scraper with respect to the surface of the grindometer changes with the thickness of the grindometer employed. Furthermore, there was little assurance that the force exerted by the scraper would be uniform along its length. In addition, the speed at which the gage was moved by the motor was not variable. Furthermore, the platform on which the gage was mounted extended beyond the confines of the machine when the grindometer was in its initial position.
The color and transparency of inks and other liquids are often compared by depositing drops of each at spaced points across the width of a sheet of paper and manually passing a scraper that is in contact with the sheet through the drops and along the length of the paper in a draw-down procedure so as to produce parallel smears. It is sometimes advantageous to have a black line extending across the width of the sheet. It is apparent that reproduceable results are difficult to attain because any slight differences in the pressure between the scraper and the paper for the two drops will cause the respective smears to have critical differences in thickness.
Whether the machine is being used to determine particle sizes or to make a comparison of color or transparency, it is important that the scraper move at a selected speed. Where particle sizes are being determined, it has been found that better results are obtained if the speed is reduced for substances of greater viscosity.